Afferent activity evoked by natural stimulation of the biliary system in the ferret

A technique for the natural stimulation of the biliary system which permits the distinction between noxious and innocuous intensities of stimulation has been developed in the ferret. Male ferrets anaesthetized with urethane have been used. Controlled distensions of the biliary system were produced and the nociceptive nature of the stimulus was ascertained by reflex increases in blood pressure. Levels of biliary pressure that did not evoke changes in blood pressure were considered innocuous. Using this approach electrical activity has been recorded from biliary afferents. Thirty-two recordings were obtained. Twenty-one were of afferents that could be excited by innocuous levels of biliary pressure (low threshold afferents) and 10 recordings were of afferents excited only by noxious stimulation of the biliary system (high threshold afferents). One fibre could not be activated by changes in biliary pressure. Twenty-seven receptive fields were located: 12 in the gallbladder and 15 in the biliary ducts. The relevance of high threshold biliary receptors to visceral nociception is discussed.